ixp4xx_eth: fix error check return value of platform_get_irq()

platform_get_irq() return negative value on failure, so null check of
return value is incorrect. Fix it by comparing whether it is less than
zero.

Fixes: 9055a2f5 ("ixp4xx_eth: make ptp support a platform driver")
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Lv Ruyi <lv.ruyi@zte.com.cn>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220412085126.2532924-1-lv.ruyi@zte.com.cnSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/xscale/ptp_ixp46x.c

@@ -271,7 +271,7 @@ static int ptp_ixp_probe(struct platform_device *pdev)
 	ixp_clock.master_irq = platform_get_irq(pdev, 0);
 	ixp_clock.slave_irq = platform_get_irq(pdev, 1);
 	if (IS_ERR(ixp_clock.regs) ||
-	    !ixp_clock.master_irq || !ixp_clock.slave_irq)
+	    ixp_clock.master_irq < 0 || ixp_clock.slave_irq < 0)
 		return -ENXIO;
 
 	ixp_clock.caps = ptp_ixp_caps;